1. Field of the Invention
This invention relates to a solder coating method for applying a solder to the outer leads of semiconductor devices and an apparatus therefor.
2. Description of the Prior Art
TAB-type semiconductor devices fabricated by mounting semiconductor elements on a flexible film such as a polyimide film and connecting their electrodes to the leads formed on the film, has a number of merits e.g., their suitability for mass production, their adaptability to miniaturization and their realizability of a fine pattern, and presently they are used widely.
In the plan view of FIG. 5 showing an example of the manufacturing process of the TAB-type semiconductor devices, numeral 1 designates a long film, 2 a plurality of device holes formed at regular intervals in the lengthwise direction of the film 1, and 3 a plurality of leads of a high-conductivity material such as copper foil formed on the film 1 with their forward ends being extended into corresponding one of the device holes 2 to form inner leads 3a. Numeral 4 designates sprocket holes for conveying the film 1. Numeral 5 designates a plurality of semiconductor elements each arranged within one of the device holes 2 and having a plurality of electrodes 6 connected to the inner leads 3a.
The film 1 having the semiconductor elements 5 connected in this way is cut off along mark-off lines 7 by a press or the like, thus producing the individual semiconductor devices. In this case, the leads on the outer side of each semiconductor element 5 are referred to as outer leads 3b. It is to be noted that there are cases where each semiconductor element 5 and a part of its outer leads 3a are packaged with a synthetic resin before the cutting.
While such semiconductor device is mounted on a substrate or a lead frame, in this case the reserve solder is usually applied to the outer leads 3b as shown by the hatching in FIG. 5 so as to facilitate positive connection thereof to the conductor pattern of the substrate or the leads of the lead frame.
FIGS. 7 and 8 are perspective views showing the conventional reserve solder coating method for TAB-type semiconductor devices. Numeral 8 designates a solder tank including discharge ports 9 and 9a on its longitudinal sides and inlet ports 8a in its bottom so that a molten solder 10 is introduced into the solder tank 8 through the inlet ports 8a to overflow through the discharge ports 9 and 9a for recirculation. The outer lead 3b portions on one side of the film 1 are dipped in the molten solder 10 and the film 1 is moved in the lengthwise direction, thus applying the solder 10 to the outer leads 3b. When the solder dipping of the outer leads 3b on one side is completed, the film 1 is turned upside down so that the outer leads 3b on the other side are dipped in the solder 10 and the film 1 is moved in the like manner, thereby applying the solder.
While the above-mentioned solder coating method is widely put in practical use owing to its merits such as the relatively simplified equipment and the increased soldering rate, the application of the solder by this conventional method is not possible in the case of a semiconductor device comprising a semiconductor element 5 having leads 3 connected to the four sides thereof as shown in FIG. 6.